Sensor with memory storing calibration information

ABSTRACT

A sensor is configured to sense a parameter of an aqueous liquid. The sensor has an analog output port configured to provide an analog signal indicative of a sensed parameter, and a calibration memory device storing individual digital information indicative of a calibration of the sensor. A digital output port provides a digital signal indicative of the digital information. A treatment system and method is matched to the sensor.

REFERENCE TO RELATED APPLICATIONS

The entire contents of the U.S. Pat. No. 8,574,413 are herebyincorporated by reference.

BACKGROUND

The present invention relates to electrochemical probes, and moreparticularly to electrochemical sensors for measuring certaincharacteristics of liquids, particularly aqueous liquids, and componentsof such sensors.

In many situations, it is desirable to monitor a variety of waterquality parameters, often at frequent intervals or even continuously.Water quality parameters include, for example, temperature, pH, freechlorine, total alkalinity, hardness, total dissolved solids, andoxidation reduction potential (ORP). Many of these parameters can bemeasured electrolytically. For ease of explanation, much of thefollowing discussion will be with reference to monitoring water qualityin a swimming pool, although it should be borne in mind that thediscussion is likewise applicable to monitoring water quality in othersettings, such as a spa, Jacuzzi™, hot tub, fountain, aquarium,sprinkler system to spray produce, water tank, or cooling tower.

Swimming pool water must be monitored vigilantly to ensure that thewater is clean and safe for use. Conventionally, this is a manualprocess carried out by the owner or other caretaker of the pool. Theprocess involves going to the pool with vials and chemicals, scoopingwater into vials, shaking the vials, and comparing the color of theresulting solutions to those on charts to determine the chemicals neededto restore proper pool chemistry. After testing, it is necessary toobtain the chemicals, measure them out, and add them to the pool water.For example, the chlorine disinfectant used to sanitize the pool mayhave been depleted by a heavy bather load, and more chlorine needed todestroy algae, waterborne germs, and oxidize organic debris introducedinto the pool water by swimmers. It is a cumbersome process, and if poolwater quality is not maintained properly, the swimmer can contractwaterborne illnesses such as diarrhea, swimmer's ear, and skininfections.

The maintenance of swimming pool water is multifaceted in the number offactors that must be controlled. Scheme A shows water quality parametersrecommended for swimming pool water.

Scheme A Water Quality Parameter Ideal Level pH 7.2 to 7.8 Free Chlorine1.0 to 3.0 ppm Total Alkalinity (buffering capacity) 80 to 120 ppm Salt2,700 to 3,400 ppm Stabilizer 60 to 80 ppm Hardness 200 to 400 ppm TotalDissolved Solids Less than 6,000 ppm Oxidation-Reduction Potential 650mV

Two critical factors in maintaining water balance are pH and freechlorine level (FCL). pH is a measurement of the concentration ofhydrogen ions in water. It is measured using a logarithmic scale from 0to 14, with pH 7 being neutral. For pool water to be in balance, the pHmust be maintained at a level between 7.2 and 7.8. At pH below 7.2, thewater is considered to be corrosive and can etch plaster and metal inequipment such as heat exchangers. Maintaining the pH higher than 7.8will increase the tendency to form scale or cloudy water due toprecipitation of calcium dissolved in the water. Higher pH will alsorender chlorine sanitizers ineffective, as discussed further below.

Addition of chlorine sanitizers such as aqueous sodium hypochloritesolution (bleach) or solid calcium hypochlorite to water generates amixture of hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻) known as“free chlorine.” The pool industry typically recommends that a freechlorine concentration of between 1.0 and 3.0 ppm be maintained in theswimming pool to provide for effective sanitation. Hypochlorous acid isa more effective disinfectant and oxidant than the hypochlorite ion, andtheir relative proportions fluctuate with the pH of the water in thepool (low pH is more acidic and high pH is more basic). At high pH, freechlorine will be mostly in the form of hypochlorite and so it will beless effective as a sanitizer. Thus, measuring free chlorine alone doesnot assure efficacy. Both the pH and free chlorine levels of swimmingpool water must be monitored to ensure that an adequate water qualitylevel is maintained.

Chlorine and bromine are both members of the same chemical family knownas halogens. While not as popular as chlorine, bromine has gained wideacceptance as a sanitizer, especially in hot tubs where the hotturbulent water tends to increase the amount of wastes in the water.Bromine tablets, sticks or caplets are usually applied through some typeof feeder device either in-line or, in some cases, as a floater-typefeeder. The two-product system relies upon the addition of small amountsof an inert sodium bromide salt, which by itself does little. The wateris then treated with an oxidizer especially suited for this purpose, orwith chlorine. The oxidizer or chlorine acts to convert sodium bromideinto “free bromine”, a mixture of hypobromous acid (HOBr) andhypobromite ion (OBr⁻). However, unlike chlorine, the amount ofhypobromous acid present is less dependent on pH. Additionally, thebromamines formed when HOBr reacts with waste in the water do not causeeye and skin irritation or foul odors.

Alternatively, there is another way of testing the water calledoxidation-reduction potential (ORP). ORP is a measure, in millivolts, ofthe tendency of a chemical substance to oxidize or reduce anotherchemical substance. A positive voltage indicates an oxidizing solutionand a negative voltage indicates a reducing solution. ORP measurementsare valid over a wide pH range, and provide an index of water qualitybased on activity of a sanitizer rather than just its quantity. Thelower oxidation potential of bromine compared to chlorine means that ORPwill not be as sensitive to the concentration of bromine as it will tochlorine. In 1988 the National Swimming Pool Institute adopted astandard of ORP value of greater than or equal to 650 mV for publicspas. An ORP greater than or equal to 650 millivolts is adequate to killviral and bacterial pathogens within seconds.

Another swimming pool water parameter that is important to determine isthe amount of total dissolved solids (TDS). TDS is the sum of allmaterials dissolved in the water, and normally runs in the range of 250ppm and higher. TDS can be salts like sodium chloride and calciumchloride, metals like iron, copper, and manganese, and dissolved organiccompounds. The guideline for the maximum amount of total dissolvedsolids allowed in pool/spa water is <6000 ppm and in at least someenvironments <1500 ppm. At elevated levels, TDS can lead to cloudy orhazy water, difficulty in maintaining water balance, reduction insanitizer activity, and foaming. It can also inhibit the sanitizerefficiency to the point that algae plumes form even though testsindicate an acceptable free chlorine level. When this problem isidentified, the only way to reduce TDS is to drain a portion of thewater and replace it with fresh water.

It is desirable to have sensors that can monitor water qualityparameters automatically and frequently, even continuously. Sensors forsuch measurements often operate on a potentiometric electrochemicalprinciple that incorporates a reference electrode and a sensingelectrode. Conventional reference electrodes for use in suchpotentiometric electrochemical measurements typically incorporate aninternal reference fill solution in contact with an electrode in contactwith a test solution through a porous junction, which allows a slow leakof the internal reference fill solution to provide the necessaryelectrolytic contact with the liquid being tested. A metal orelectrochemical electrode in contact with the test solution completesthe circuit and an electrical potential on the reference electroderemains relatively constant while the sensing electrode responds tochemical changes in the test solution.

Conventional sensors of this type suffer from several drawbacks whenapplied to certain measurement environments. One problem is thatchemicals employed to sanitize the water can interfere with themeasurements. Conventional electrodes of this type suffer from severaldrawbacks when applied to certain measurement environments, such aslong-term unattended monitoring of pool or spa water. For example,because leakage of the internal reference fill solution through theporous junction into the tested environment is necessary to provideelectrolytic conductivity between the internal reference fill solutionand the tested environment, the useful life of the reference electrodeis limited. Moreover, a high rate of leakage is desirable to produce alow electrical impedance of the reference electrode. Moreover, in a pipemounted system, the flow of test solution flowing over the electrodeexacerbates the high leakage rate. Thus, while low electrical impedanceis desirable for accurate measurements because it reduces noise, thehigh leakage rate employed in such conventional reference electrodes toproduce the desired low electrical impedance severely limits the life ofthe electrode and the electrode must be frequently refilled with freshinternal solution or replaced.

Such conventional reference electrodes suffer from other disadvantagesas well. For example, they tend to be fragile, typically being encasedin glass. Moreover, they often are limited in operational orientation.In other words, because the reference fill solution of the electrode isa liquid, it readily flows as a result of gravity. Thus, the relativeorientation of the electrode with respect to the reference fill solutionand the reference fill solution with respect to the porous junctiondepends on the spatial orientation of the electrode and so the electrodeassembly in the test solution must be oriented vertically so that thereference fill solution is properly oriented in the electrode. Indeed,silver/silver chloride reference electrodes suspended in glass-encasedfill solutions have been employed in combination with antimonyelectrodes in some pH sensors, with all the attendant disadvantages ofglass membranes and fill solutions noted above.

What is needed are sensors that are precise and reliable and canaccurately monitor various water quality parameters such as pH, freechlorine level, ORP, and TDS over an extended period of time. Inparticular, it would be desirable to have sensors that are individuallycalibrated and have their own memory device. Further, it would bedesirable to interface such sensors with control equipment so thatappropriate water quality adjustments can be made to ensure the water ishealthful. The plurality of sensors of the present invention is robustand provide for long periods of unattended operation.

SUMMARY

In one form, a sensing device comprises a sensor configured to sense afirst parameter and a second parameter of a liquid and having an analogoutput port configured to provide a first analog signal indicative ofthe sensed first parameter and configured to provide a second analogsignal indicative of the sensed second parameter. The sensor has acalibration memory device storing individual digital informationindicative of a calibration of the first parameter relative to thesecond parameter and has a digital output port providing a digitalsignal indicative of the digital information.

In another form, a treatment system and/or method employ the sensor.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system according to one embodiment of theinvention illustrating, schematically, a measurement system combiningthree sensors of the present invention in a pool treatment situation.

FIG. 2 is a schematic diagram of a chlorine sensor circuit.

FIG. 3 is a schematic diagram of a TDS sensor circuit.

FIG. 4 is a schematic diagram of an ORP sensor circuit.

FIG. 5 is a schematic diagram of a pH sensor circuit.

FIG. 6 is a block diagram of sensors and a system control unit accordingto an embodiment of the invention.

FIG. 7 is a perspective view of a sensor according to one embodiment ofthe invention.

FIG. 8 is cross-sectional view taken along lines 8-8 of FIG. 9.

FIG. 9 is right side view of the sensor of FIG. 7.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

The present invention comprises sensors, each of which is individuallycalibrated and has its own memory device storing individualizedcalibration information. For example, such sensors comprise chlorinesensors, total dissolved solids (TDS) sensors, oxygen reductionpotential (ORP) sensors, and/or pH sensors. The present invention alsocomprises systems and methods which use such sensors. The varioussensors of the present invention may be employed in system combinationsin any desired permutation. For example, a pH sensor may be used aloneor in combination with a chlorine sensor, an ORP sensor, and/or a TDSsensor. Other sensors, such as a temperature sensor, can be employed inany of such combinations.

FIG. 1 illustrates, schematically, a measurement system combining threesensors of the present invention in a pool treatment situation. As canbe seen from FIG. 1, water from a pool 100 is pumped via pump 102through a filter 104 and then a flow sensor 106, to a chlorine sensor(i.e. measures free chlorine level, FCL) 108, a pH sensor 110, and anORP sensor 112 of the present invention. The output from the sensors106, 108, 110, and 112 are sent to a system control unit 114, alsocontrolled by an external interface 116 (such as a mobile device orcomputer having a display), which can enter adjustments and desiredsettings, such as desired pH or chlorine content of the pool water, intothe system control unit 114. The flow sensor 106 is used to compensatethe signal on the chlorine sensor since the output of the chlorinesensor is proportional to the flowrate. This compensation is animportant feature when using variable speed pumps. The system controlunit 114 controls a sensor manifold 118 and control pumps (or valves)120 and 122, which, according to instructions from system control unit114 (and external interface 116), meter pH-adjusting chemicals andchlorine from supply tanks 124 and 126, respectively, into the waterpumped from the pool, after which the water is recycled back into pool100.

In one embodiment of the sensor there is a memory circuit (such as anEEPROM) placed inside the sensor housing. The memory circuit is used tostore calibration and other information such as device identification(ID) and/or a serial number. The central benefit of this configurationis that it provides a high level of traceability to the measurementsystem. It also allows for storing other user defined data.

FIG. 6 is a block diagram of sensors and a system control unit accordingto an embodiment of the invention. In one form, FIG. 6 illustrates atreatment system 600 for treating a liquid such as an aqueous liquid602. A conduit 604 channels the aqueous liquid 602 to be treated. Atreatment device 606 associated with the conduit alters the aqueousliquid 602 and has an input port 608 for receiving a treatment signalindicative of an extent to which the treatment device 606 alters theaqueous liquid 602. For example, the treatment device 606 can be achlorine pump 610A having a control input port 608A and/or an acid pump610B having a control input port 608B. One or more sensors 612 sense aparameter of the aqueous liquid 602 and have an analog output port 614providing analog signals indicative of the sensed parameters. Forexample, the sensor 612 can be a chlorine sensor 616A, a pH sensor 616B,an ORP sensor 616C, and/or a TDS sensor 616D located within the conduit604 (e.g., within a manifold). Each sensor has a calibration memorydevice 618 (e.g., an EEPROM or a tangible, non-transitory storagememory) storing digital information indicative of a calibration of thesensor 616 and has a digital output port 621 providing a digital signalindicative of the digital information. In addition, each sensor 612senses a second parameter of the aqueous liquid 602 and provides asecond analog signal via analog output port 614 indicative of secondsensed parameter. For example, the second parameter comprisestemperature of the aqueous liquid 602 in which case the calibrationmemory device 618 (e.g., an EEPROM) stores digital informationindicative of a temperature-compensated calibration of the sensor 616and has a digital output port 621 providing a digital signal indicativeof the digital information. In one embodiment, the calibration memorydevice 618 is an integral part of the sensor 612 so that the calibrationmemory device 618 is embedded within the sensor 612 and enclosed by thesensor 612, such as illustrated in FIGS. 7-9. Thus, the calibrationmemory device 618 and the sensor 612 comprise a unitary component withina housing.

A system control unit, i.e., controller 620, has a digital input port622 connected to the digital output port 621 of the sensor 616. Thecontroller 620 receives the digital signal via its digital input port622 and determines a calibration of the sensor 612. The controller 620has an analog input port (e.g. an analog-to-digital (A/D) converter 624)connected to the analog output port 614 of the sensor 612. Thecontroller 620 receives the analog signal via its analog input port anddetermines the parameter of the aqueous liquid based on the receivedanalog signal and based on the received digital signal. The controllerhas an output port connected to the treatment device 606 providing thetreatment signal to the input port of the treatment device. Thetreatment signal is configured to control the treatment device 606 as afunction of the determined parameter by controlling the extent to whichthe treatment device alters the aqueous liquid 602.

The treatment device 606 in one form comprises a chlorine supplier suchas chlorine pump 610A or a chlorine generator for adding free chlorineto the aqueous liquid 602. The treatment signal is indicative of anamount of free chlorine added to the aqueous liquid or is indicative ofa rate at which free chlorine is added to the aqueous liquid. The sensorcomprises a chlorine sensor 616A sensing a free chlorine level of theaqueous liquid 602 and the analog signal is indicative of the freechlorine level of the aqueous liquid. The controller 620 determines thefree chlorine level of the aqueous liquid 602 based on the receivedanalog signal and based on the received digital signal. The treatmentsignal provided by the output port (e.g., a digital-to-analog (D/A)converter 626) of the controller is configured to control the chlorinesupplier as a function of the determined free chlorine level of theaqueous liquid 602 as compared to a minimum free chlorine level bycontrolling the amount of free chlorine added to the aqueous liquid 602by the chlorine supplier or the rate at which free chlorine is added tothe aqueous liquid 602 by the chlorine supplier.

In one form, the treatment device 606 comprises an acid supplier such asacid pump 610B for adding acid to the aqueous liquid. The treatmentsignal is indicative of an amount of acid added to the aqueous liquid oris indicative of a rate at which acid is added to the aqueous liquid.The sensor 612 comprises a pH sensor 616B sensing a pH level of theaqueous liquid and wherein the analog signal is indicative of the pHlevel of the aqueous liquid. The controller 620 determines the pH levelof the aqueous liquid based on the received analog signal and based onthe received digital signal. The treatment signal provided by the outputport of the controller is configured to control the acid supplier as afunction of the determined pH level of the aqueous liquid as compared toa maximum pH level by controlling the amount of acid added to theaqueous liquid by the acid supplier or the rate at which acid is addedto the aqueous liquid by the acid supplier.

In one form, the treatment device 606 comprises a chlorine supplier suchas chlorine pump 610A for adding free chlorine to the aqueous liquid602. The treatment signal is indicative of an amount of free chlorineadded to the aqueous liquid 602 or is indicative of a rate at which freechlorine is added to the aqueous liquid 602. The sensor 612 comprises anORP sensor 616 sensing a free chlorine level of the aqueous liquid 602.The analog signal is indicative of the free chlorine level of theaqueous liquid.

The controller 620 determines the free chlorine level of the aqueousliquid 602 based on the received analog signal and based on the receiveddigital signal. The treatment signal provided by the output port 626 ofthe controller is configured to control the chlorine supplier as afunction of the determined free chlorine level of the aqueous liquid 602as compared to a minimum free chlorine level by controlling the amountof chlorine added to the aqueous liquid by the chlorine supplier or therate at which free chlorine is added to the aqueous liquid by the acidsupplier.

Each of the above sensors 612 includes a temperature sensing device 628sensing a temperature of the aqueous liquid 602. For ease ofillustration, the temperature sensing device 628 is illustratedseparately in phantom in FIG. 6. It is understood that each of thechlorine sensor 616A, the pH sensor 616B, the ORP sensor 616C, andoptionally the TDS sensor 616D each have a temperature sensing devicesuch as a thermistor, as illustrated in FIGS. 7-9. The analog outputport 614 provides a temperature signal indicative of the sensedtemperature, although it is contemplated that the temperature sensingdevice can provide a digital signal via digital output port 621. Foranalog temperature sensing devices, the controller 620 receives thetemperature signal via A/D converter 624. For digital temperaturesensing devices, the controller 620 receives the temperature signal viadigital input port 622. The controller 620 determines the temperature ofthe aqueous liquid 602 based on the temperature signal, and provides thetreatment signal as a function of the determined temperature.

In one form, the sensor comprises a TDS sensor (see FIG. 3) sensing aTDS ppm salt level of the aqueous liquid 602. The analog signal 614 isindicative of the TDS ppm salt level of the aqueous liquid 602. Thecontroller 602 determining the TDS ppm salt level of the aqueous liquid602 based on the received analog signal and based on the receiveddigital signal, the controller 602 provides an indication such as anotice on the external interface 116 and/or an alarm when the determinedTDS ppm salt level of the aqueous liquid 602 is greater than a maximum.

As shown in FIGS. 2-5, the calibration memory device comprises an EEPROM(e.g., DS2341) storing some or all of the following temperaturecompensation information (see Table 2 below): a high or low gain, anoffset, and an analog-to-digital conversion value of the analog signalindicative of the sensed parameter. In FIGS. 2-5, the solder pads arenumbered the same as the connector for clarity. Terminals 1 and 2 of theEEPROM DS2341 are connected to terminals 5 and 6 of the connector whichis connected to the controller 620 providing and/or receiving the storeddigital information. Terminal 1 is a ground port and terminal 2 is aninput/output (I/O) port.

The other terminals of the EEPROM DS2341 are not used. In general, eachsensor 612 measures two parameters of a liquid such as an aqueous liquidand the calibration memory device stores information to calibrate oneparameter relative to the other parameter.

Alternatively or in addition, the EEPROM stores the followinginformation: two or more temperature coefficients for adjusting theanalog signal indicative of the sensed parameter, and/or the controller620 includes a controller calibration memory device 634 in which thecontroller 620 reads the sensor calibration memory device 618 and storesthe digital information stored in the calibration memory device 634 ofthe sensor 612. As a default, the controller can be configured tocalibrate the sensor 612 in the event that the digital informationstored in the calibration memory device 618 of the sensor is not valid,or the controller is configured with a memory device (not shown) havingdefault calibration information in the event that the digitalinformation stored in the calibration memory device 618 of the sensor612 is not valid. Optionally, the digital information stored in thecalibration memory device 618 of the sensor 612 is encrypted and thecontroller 620 is configured to decrypt the encrypted digitalinformation.

Optionally, the controller 620 stores a plurality of identificationinformation identifying selected sensors 612. The controller 620 isconfigured to disable an operation of the system 600 if the calibrationmemory device 618 of the sensor 612 having its digital output port 614connected to the digital input port 622 of the controller 620 does nothave identification information which corresponds to (e.g. matches) theidentification information stored in the controller memory device 634.As a result, only selected sensors 612 will operate with selectedsystems 600 to prevent a mismatch between a sensor 612 and the system600 to which it is connected.

In one form, controller 620 is a microcontroller which communication tothe memory 618 on each sensor 612 using a simple two wire connection onthe sensor connector. (See the schematics illustrated in FIGS. 2-5) Astandard method based on the “1-Wire Protocol” such as implemented usinga MAXIM DS2431 or similar circuitry can be used as the method ofcommunication. The microprocessor detects when a sensor 612 is connectedand retrieves the information from its EEPROM 618. Executable softwarestored in memory 636 prompts for overwrite then processes the input dataand displays it on an LCD or other display device (such as a display ofthe external interface 116, not shown). Each circuit also has acommunication port available to connect to an external interface 116 toread/write the EEPROM data for manual editing. The EEPROM data can beencrypted to prevent viewing/editing without authorization.

In one form, the communication is through a “one wire” interface (suchas IEEE P1451.4 Smart Sensor Interface) provided by a DallasSemiconductor Corp DS2431 1-wire EEPROM. The interface uses a pull-upresistor from the I/O line of a microcontroller to both power the deviceand communicate with it. (See APPLICATION NOTE 2966 MINIMAL REMOTE1-WIRE® MASTER Protocol from Maxim Integrated Circuits and DS2431Datasheet.)

Each sensor 612 can be assigned its own unalterable and unique 64-bitROM registration number that is factory lasered into the chip. Thisgives every sensor 612 a unique identification number. In this case eachsensor will have a unique “serial number”.

The following Table 1 illustrates the various parameters detected by thesensors 612.

TABLE 1 Desired Chemical Sensor Analyte Level Treatment Example(s) pHHydrogen ions A current Muriatic acid, a The Hayward AQL- FIG. 5 signalsolution of CHEM-2-240 is a CO₂ indicative hydrogen chloride dispensingsystem. To of a pH in water, is added lower pH, a manifold of 7.2 to tolower pH. The connects to a carbon 7.8 acid feed system dioxide tank.CO₂ is a 4:1 dilution of reduces pH by forming 20 degree Baume carbonicacid (H₂CO₃). hydrochloric acid Alternatively, the Sense (31.45 wt. %)in and Dispense system water. supports the Stenner The Baume scale Pumpacid feed system. measures the AQL-CHEM-3-120 is an density of liquidsautomatic acid heavier than dispensing system to water. The lower the pHlevel of Baume of pool water. It utilizes a distilled water is Stenner0. Hydrochloric S1G45MJL3F2S/W2S acid is available series acid pump and15 in concentrations gallon tank. ranging from 4 to 23 degree Baume. ORP“Free chlorine”—a A voltage Generate “free AQL-CHEM is a pH and FIG. 4combination of signal chlorine” from ORP sensing kit which hypochlorousacid ≧650 mV NaCl. uses a chlorine generator (HOCl) and to increase thelevel of hypochlorite ion free chlorine. (OCl⁻) providing a A chlorinegenerator millivolt level (also known as a salt primarily indicativecell, salt generator, or of an oxidizing salt chlorinator) uses power ofthe water electrolysis in the presence of dissolved salt (NaCl) toproduce hypochlorous acid (HOCl) and sodium hypochlorite (NaOCl).Chlorine “Free chlorine”—a A current Generate “free Same as ORP. FIG. 2combination of signal chlorine” from hypochlorous acid (HOCl) indicativeNaCl. and hypochlorite ion (OCl⁻). of 1.0 to 3.0 ppm. TDS A salt levelindicative of A current None. To Hayward FIG. 3 Total DissolvedSolids-all signal reduce TDS, a Sense and conductive materialsindicative portion of the Dispense dissolved in the water. of <6000water must be Chemistry Responsive to salts like ppm drained andAutomation sodium chloride and or replaced with calcium chloride,minerals A current fresh water. like copper, iron, and signal manganese,and electro- indicative active ionic materials. of <1500 ppm.

Typical Sequence of Operation New Sensor Connection

If no sensor is connected, the controller 620 continually issues a resetsignal (I/O Line low for 480 μs) and waits for the Presence signalconsisting of the Slave pulling the line low within 60 μs from the timethe controller 620 releases the line. When the controller 620 senses thepresence of a sensor 612, it goes through an ID process that reads thesensor file in memory 618 and makes sure that the correct sensor isattached. The controller 620 then copies the calibration and IDinformation into its' own internal memory 634. It then prompts tooverwrite the current calibration file.

In one form, the software in memory 636 can notify a user if the sensoris different from the one it remembers. If there is not a validcalibration file in the sensor, the operator can be given two choices.Calibrate or Use raw ADC (default) values. If Calibration is chosen, theinstrument will go into CALIBRATION MODE in which the sensor isrecalibrated.

Calibration Procedure Sequence

Table 2 below indicates one embodiment for a table layout of calibrationparameters and the number of bytes allocated for each for memory 618.

TABLE 2 Size Description Type (Bytes) High Gain float 4 Offset float 4ADC word 2 Temperature*10 word 2 Low Gain float 4 Offset float 4 ADCword 2 Temperature*10 word 2 Temp Comp coeff a float 4 coeff b float 4coeff c float 4 Date Month byte 1 Day byte 1 Year-2000 byte 1 ID SensorType byte 1 Version word 2 Status byte 1 Checksum byte 1 Used 44Available bytes 128 Free 84

In one form, some or all of the information in memory 618 can beencrypted to prevent reverse engineering. The calibration information inthe memory 618 is used to convert the ADC values from the sensor alongwith the current temperature to calculate the desiredtemperature-compensated output variable (e.g., Free Chlorine, TDS, pH,ORP).

The calibration record of each sensor includes the signal level (in theunits of the type of sensor) and the temperature at which it wasmeasured at a high level of concentration and at a low level ofconcentration. Chlorine sensors are calibrated at a constant pH between7.2 and 7.6.

As one example, chlorine sensor 616A may be calibrated as follows. Thesensor 616A is tested at a first known temperature and at a first knownFCL level and the millivolt level at its analog output port 614Aindicative of the chlorine level is read and saved. The thermistor 710of the chlorine sensor 616A can be used to determine the firsttemperature. As a specific example of this first reading, a sensor 616Aat temperature 26.8° C. and at an FCL level of 0.40 ppm provides a first262.51 mV output. The sensor 616A is again tested at a second knowntemperature (which may be different from the first temperature) and at asecond known FCL level (different from the first FCL level) and themillivolt level at its output 614A is read and saved. As a specificexample of this second reading, the same sensor 616A at temperature26.2° C. and at an FCL level of 3.40 ppm provides a second 481.07 mVoutput. The temperature readings can be determined by reading thethermistor 628 of the sensor 616A. The first and second readings arestored in the calibration memory 618A. The first known temperature, thefirst known FCL, and the resulting first mV output reading are enteredinto a table, as shown in Table 3 below. The second known temperature,the second known FCL, and the resulting second mV output reading areentered into the same table. Additional readings are extrapolated fromthe first and second readings and added to the table to provide acalibration table with automatic temperature compensation. Thiscalibration table is used by the system control unit 620 to scale the mVreadings and then derive the chlorine concentration from the chlorinesensor 616A. Alternatively or in addition, the first and second readingsare used to define an algorithm which is then used to interpret readingsfrom the chlorine sensor 616A. The table and/or algorithm can be storedin the calibration memory 618A and/or can be part of the system controlunit 620.

TABLE 3 Temp 1 26.8° C. FCL 1 0.40 ppm mV 1 262.51 Temp 2 26.2° C. FCL 23.40 ppm mV 2 481.07

By recalling both the first and second known temperature values, thefirst and second known FCL values, and the first and second known mVreadings, the system control unit 620 derives a linear formula ofchlorine values in the form of Y=mX+b, wherein Y can be defined as FCLlevel or temperature compensated mV reading and X is defined as theopposite value. Both m and b values are then stored into memory onsensor 616A and recalled by the system control unit 620 to calculate FCLreading from the current mV value output by sensor 616A, if needed. Asan example, if Y is defined as FCL level, then X is defined astemperature compensated mV reading. To define m, the system control unit620 will divide the difference between the second known FCL level (3.40)and the first known FCL level (0.40) by the difference between thesecond known mV level (481.07) and the first known mV level (262.51).The system control unit 620 will use substitution to define b for theabove formula by using the second known FCL level (3.40) as X, thesecond known mV level (481.07) as Y, and m as defined above.

As another example, pH sensor 616B may be calibrated as follows. Thesensor 616B is tested at a first known temperature and at a first knownpH level and the millivolt level at its analog output port 614Bindicative of the pH level is read and saved. The thermistor 710 of thepH sensor 616B can be used to determine the first temperature. As aspecific example of this first reading, a sensor 616B at temperature26.8° C. and at a pH level of 6.91 provides a first 2158.73 mV output.The sensor 616B is again tested at a second known temperature (which maybe different from the first temperature) and at a second known pH level(different from the first pH level) and the millivolt level at itsoutput 614B is read and saved. As a specific example of this secondreading, the same sensor 616B at temperature 26.2° C. and at a pH levelof 7.77 provides a second 2424.91 mV output. The temperature readingscan be determined by reading the thermistor 628 of the sensor 616B. Thefirst and second readings are stored in the calibration memory 618B. Thefirst known temperature, the first known pH, and the resulting first mVoutput reading are entered into a table, as shown in Table 4 below. Thesecond known temperature, the second known pH, and the resulting secondmV output reading are entered into the same table. Additional readingsare extrapolated from the first and second readings and added to thetable to provide a calibration table with automatic temperaturecompensation. The calibration table is used by the system control unit620 to scale the mV readings and then derive the pH level from the pHsensor 616B. Alternatively or in addition, the first and second readingsare used to define an algorithm which is then used to interpret readingsfrom the pH sensor 616B. The table and/or algorithm can be stored in thecalibration memory 618B and/or can be part of the system control unit620.

TABLE 4 Temp 1 26.8° C. pH 6.91 mV 1 2158.73 Temp 2 26.2° C. pH 7.77 mV2 2424.91

By recalling both the first and second known temperature values, thefirst and second known pH values, and the first and second known mVreadings, the system control unit 620 derives a linear formula of pHvalues in the form of Y=mX+b, wherein Y can be defined as pH level ortemperature compensated mV reading and X is defined as the oppositevalue. Both m and b values are then stored into memory on sensor 616Band recalled by the system control unit 620 to calculate pH reading fromthe current mV value output by sensor 616B, if needed. As an example, ifY is defined as pH level, then X is defined as temperature compensatedmV reading. To define m, the system control unit 620 will divide thedifference between the second known pH level (7.77) and the first knownpH level (6.91) by the difference between the second known mV level(2424.91) and the first known mV level (2158.73). The system controlunit 620 will use substitution to define b for the above formula byusing the second known pH level (7.77) as X, the second known mV level(2424.91) as Y, and m as defined above.

As another example, ORP sensor 616C may be calibrated as follows. ForORP, a reference chlorine measurement is made and stored relative to aspecific mV output from sensor 616C. Measurements are repeated atregular intervals (6 months or 1 time/season) to gauge sensor drift.There is no computational derivative of the values stored in sensor616C.

As another example, TDS sensor 616D may be calibrated as follows. Thesensor 616D is tested at a first known temperature and at a first knownpH level and the millivolt level at its analog output port 614Dindicative of the TDS level is read and saved. The thermistor 710 of theTDS sensor 616D can be used to determine the first temperature. As aspecific example of this first reading, a sensor 616D at temperature26.8° C. and at a TDS level of 918 ppm provides a first 545.79 mVoutput. The sensor 616D is again tested at a second known temperature(which may be different from the first temperature) and at a secondknown TDS level (different from the first TDS level) and the millivoltlevel at its output 614D is read and saved. As a specific example ofthis second reading, the same sensor 616D at temperature 26.2° C. and ata TDS level of 3430 ppm provides a second 1960.93 mV output. Thetemperature readings can be determined by reading the thermistor 628 ofthe sensor 616D. The first and second readings are stored in thecalibration memory 618D. The first known temperature, the first knownTDS, and the resulting first mV output reading are entered into a table,as shown in Table 5 below. The second known temperature, the secondknown TDS, and the resulting second mV output reading are entered intothe same table. Additional readings are extrapolated from the first andsecond readings and added to the table to provide a calibration tablewith automatic temperature compensation is used by the system controlunit 620 to scale the mV readings and then derive the TDS level from theTDS sensor 616D. Alternatively or in addition, the first and secondreadings are used to define an algorithm which is then used to interpretreadings from the TDS sensor 616D. The table and/or algorithm can bestored in the calibration memory 618D and/or can be part of the systemcontrol unit 620.

TABLE 5 Temp 1 26.8° C. TDS  918 ppm mV 1  545.79 Temp 2 26.2° C. TDS3430 ppm mV 2 1960.93

By recalling both the first and second known temperature values, thefirst and second known TDS values, and the first and second known mVreadings, the system control unit 620 derives a linear formula of TDSvalues in the form of Y=mX+b wherein Y can be defined as TDS level ortemperature compensated mV reading and X is defined as the oppositevalue. Both m and b values are then stored into memory on sensor 616Dand recalled by the system control unit 620 to calculate pH reading fromthe current mV value output by sensor 616D, if needed. As an example, ifY is defined as TDS level, then X is defined as temperature compensatedmV reading. To define m, the system control unit 620 will divide thedifference between the second known TDS level (3430 ppm) and the firstknown TDS level (918 ppm) by the difference between the second known mVlevel (1960.93) and the first known mV level (545.79). The systemcontrol unit 620 will use substitution to define b for the above formulaby using the second known TDS level (3430 ppm) as X, the second known mVlevel (1960.93) as Y, and m as defined above.

The conductivity of the aqueous liquid is proportional to theconductivity so that an increase in current is indicative of an increasein total dissolved solids (TDS).

In one embodiment, ORP sensors are only checked for sufficient spanusing a quinhydrone solution mixed with two different pH buffers. SinceORP sensors do not necessarily need calibration, ORP sensor calibrationmemory 618C is optional. Even without calibration information, the ORPsensor calibration memory 618C is useful for providing identity andtracking information for each ORP sensor.

Each time a sensor is connected, the microprocessor of the controller620 detects the presence of the sensor through the 1 wire interface. Itthen is queried for the calibration information which is compared to thecalibration file held in its own internal flash memory. If it is thesame no action is taken. If it is different, it prompts to overwrite theprevious record.

The sensor 612 can be configured for use with a Hayward Sense andDispense system, which uses a salt chlorine supplier which generateschlorine by placing a DC current across two electrodes which separatesthe chlorine from the sodium chloride (NaCl). The chlorine supplier iscontrolled by the ORP sensor. The pH is controlled by monitoring the pHwith a probe based on standard pH probe construction and actuating avalve on an acid tank to inject the proper amount of acid to maintainthe pH at the desired level. Since the action of the chlorine supplierraises the pH over time, there is a need for addition of acid to keepthe pH in bounds.

In one form, the sensors 612 supplant sensors currently in use alongwith the attendant hardware and software to provide more accuracy andlongevity.

Adjustment of Levels

In one form, controller 620 stores a given amount of chemicals needed tochange either the pH level or ORP level of the water to a desired level.Various automated chemical dispensing systems to adjust pH/ORP areprovided, for example, by Hayward Industries Inc. (Elizabeth, N.J.).Hayward Sense and Dispense® technology provides chemistry kits forsampling pH and free chlorine levels and adjusting chemical feeding. TheSense and Dispense® system uses a proportional feed algorithm thatcontinuously tests the water, samples pH and sanitizing activity, andadjusts chemical feeding on a basis proportional to the demand.

Sense and Dispense® consists of two kits. The first is AQL-CHEM, a pHand ORP sensing kit which uses a chlorine generator to increase thelevel of free chlorine. The chlorine generator, also known as salt cell,salt generator, or salt chlorine supplier, uses electrolysis in thepresence of dissolved salt (NaCl) to produce hypochlorous acid (HOCl)and sodium hypochlorite (NaOCl), which are the sanitizing agentscommonly used in swimming pools.

The adjustment of pH can be achieved using a second kit, AQL-CHEM2,which includes a manifold that connects to a carbon dioxide (CO₂) tankto inject carbon dioxide into the pool water. Carbon dioxide reduces pHto recommended levels by forming carbonic acid (H₂CO₃), a weak acid thatwill lower the pH of the pool water slowly without the safety or healthconcerns normally associated with stronger acids. As an alternative tocarbon dioxide, the Sense and Dispense® system also supportscommercially available peristaltic acid pumps. With AQL-CHEM3, a StennerPump acid connected to a 15 gallon tank lowers the pool water pH byintroduction of muriatic acid (aqueous hydrochloric acid).

FIG. 7 is a perspective view of a sensor according to one embodiment ofthe invention. FIG. 8 is cross-sectional view taken along lines 8-8 ofFIG. 9. FIG. 9 is cross-sectional view taken along lines 9-9 of FIG. 7.The sensor 612 includes an anode 702 sealed in a tube 703 comprising aproton exchange membrane such as a copolymer of tetrafluoroethylene(e.g., a Nafion™ tube) and a cathode 704 spaced from the anode 702. Theanode 702 and cathode 704 are supported by and wrapped over a wall 706of an insulative housing 708 with sealing gasket 709 (e.g., an o-ring)which also supports a temperature sensing device such as a thermistor710 having a resistance which varies with temperature. Thermistorelectrodes TH1 and TH2 are connected to the thermistor 710 and to thesystem control unit 620 via a wire harness (not shown). In oneembodiment, the thermistor 710 has a small amount of current runningthrough it, e.g., a bias current, which is sent by the system controlunit 620. The system control unit 620 converts resistance changes tovoltage changes by using a current source to apply a bias current acrossthe thermistor to produce a control voltage. It is contemplated thatthermistor 710 can be any temperature sensing device providing a signalindicative of the temperature of the device.

A printed circuit board 712 has twelve plated through holes connected toa circuit printed on a surface of the board 712. Six plated throughholes in the board 712 receive and electrically connect to one end ofsix wires 714; the other end of the wires connect to the electricalconnector block of the circuits illustrated in FIGS. 2-5. The electricalconnector block is connected to system control unit 114, 620 (shown inFIGS. 1 and 6) by a wire harness (not shown). In FIG. 8, only threewires 714A, 714B, 714C of the six wires 714 are illustrated.

Two plated through holes in the board 712 receive and electricallyconnect to electrodes (not shown) of the calibration memory device 618which is mounted on the board 712. Two plated through holes in the board712 receive and electrically connect to the thermistor electrodes TH1and TH2. Two plated through holes in the board 712 receive andelectrically connect to the anode 702 and cathode 704. Thus, the sixwires 714 are connected to the calibration memory device 618, thethermistor electrodes TH1, TH2, and to the anode 702 and cathode 704 viathe circuit printed on the surface of the board 712.

In one form, the sensor 612 comprises a chlorine sensor comprising agold cathode 704 and a platinum anode 702 sealed within a tubecomprising a proton exchange membrane such as a copolymer oftetrafluoroethylene. The tube provides a barrier to oxygen and anionsfrom the environment exterior to the tube except as may pass through thetube. A voltage source is configured for applying a bias voltage (e.g.,350 millivolts) between the anode and the cathode, wherein a positivevoltage is applied to the anode and a negative voltage is applied to thecathode. The chlorine sensor output is a current signal which isindicative of the free chlorine in the aqueous liquid. The currentsignal is temperature dependent so that the EEPROM provides to thesystem control unit the necessary information to calibrate the currentsignal based on the temperature of the aqueous liquid.

In one form, the sensor 612 comprises a thermistor 720 and a pH sensorcomprising: (i) a gel-filled reference electrode (e.g., anode 704); and(ii) a sensing electrode (e.g., cathode 702) of antimony/antimony oxideor bismuth/bismuth oxide having an electroactive surface sealed within atube comprising a proton exchange membrane such as a copolymer oftetrafluoroethylene that provides a barrier for the sensing electrode toboth oxygen and anions from the environment exterior to the tube. The pHsensor output is a current signal which is indicative of the pH of theaqueous liquid. The current signal is temperature dependent so that theEEPROM provides to the system control unit the necessary information tocalibrate the current signal based on the temperature of the aqueousliquid.

In one form, the sensor 612 comprises a thermistor 720 and a halogensensor such as a chlorine sensor comprising a metal anode 702 shieldedby a low electrical resistance, water-permeable, oxygen barriercomprising a tube comprising a proton exchange membrane such as acopolymer of tetrafluoroethylene that provides a barrier for the sensingelectrode to both oxygen and anions from the environment exterior to thetube. A voltage source is configured for applying a bias voltage (e.g.,350 millivolts) between the anode and the cathode, wherein a positivevoltage is applied to the anode and a negative voltage is applied to thecathode. The halogen sensor output is a current signal which isindicative of the halogen in the aqueous liquid. The current signal istemperature dependent so that the EEPROM provides to the system controlunit the necessary information to calibrate the current signal based onthe temperature of the aqueous liquid.

In one form, the sensor 612 comprises a total dissolved solids (TDS)sensor comprising a pair of spaced-apart electrodes configured to beexcited by a sine wave voltage of 16 kHz at 1V AC excitation voltage. Acurrent amplifier and rectifier electrically responsive to the pair ofspaced-apart electrodes generate a voltage indicative of the voltagebetween the spaced-apart electrodes. A converter electrically responsiveto the voltage indicative of the voltage between the spaced-apartelectrodes converts the indicative voltage for at least one of displayand processing. A display electrically responsive to the converterdisplays a total dissolved solids measurement in the aqueous solution inwhich the pair of spaced apart electrodes is placed. The TDS sensoroutput is a current signal which is indicative of the TDS of the aqueousliquid. The TDS of the aqueous liquid is proportional to itsconductivity so that an increase in current is indicative of an increasein total dissolved solids (TDS).

The current signal indicating TDS is generally insensitive totemperature for aqueous liquids so the EEPROM provides other informationsuch as device identification (ID) and/or a serial number. In the eventthat the current signal is temperature dependent for the TDS of aparticular fluid being sensed, the TDS sensor can include a thermistor710 and the EEPROM provides to the system control unit the necessaryinformation to calibrate the current signal based on the temperature ofthe aqueous liquid.

In one form, the sensor 612 comprises an ORP sensor comprising a goldcathode 704 and a platinum anode 702 sealed within a tube comprising aproton exchange membrane such as a copolymer of tetrafluoroethylene. Thetube provides a barrier to oxygen and anions from the environmentexterior to the tube except as may pass through the tube. The ORP sensoroutput is a voltage signal which is indicative of the oxidizing power ofthe aqueous liquid. The voltage signal is temperature dependent so thatthe EEPROM provides to the system control unit the necessary informationto calibrate the voltage signal based on the temperature of the aqueousliquid.

Thus, the present invention comprises sensors 612, each of which isindividually calibrated and has its own memory device 618 storingindividualized calibration information which is unique to the individualdevice. In one embodiment, each sensor 612 is calibrated at a productionfacility before the sensor 612 is installed within a system 600 so thatthe calibration information stored in memory device 618 is unique to thesensor 618 and independent of any system in which the sensor 618 isinstalled. In one embodiment, each sensor 612 is calibrated by areference system at a production facility before the sensor 612 isinstalled within a system 600 so that the calibrated sensors 618 areconsistent with each other and the sensors 618 provide substantially thesame output independent of the environment or system within which thesensors 618 are installed.

The Abstract and summary are provided to help the reader quicklyascertain the nature of the technical disclosure. They are submittedwith the understanding that they will not be used to interpret or limitthe scope or meaning of the claims. The summary is provided to introducea selection of concepts in simplified form that are further described inthe Detailed Description. The summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used as an aid in determining the claimed subject matter.

For purposes of illustration, programs and other executable programcomponents, such as the operating system, are illustrated herein asdiscrete blocks. It is recognized, however, that such programs andcomponents reside at various times in different storage components of acomputing device, and are executed by a data processor(s) of the device.

Although described in connection with an exemplary computing systemenvironment, embodiments of the aspects of the invention are operationalwith numerous other computing system environments or configurations. Thecomputing system environment is not intended to suggest any limitationas to the scope of use or functionality of any aspect of the invention.Moreover, the computing system environment should not be interpreted ashaving any dependency or requirement relating to any one or combinationof components illustrated in the exemplary operating environment.Examples of well-known computing systems, environments, and/orconfigurations that may be suitable for use with aspects of theinvention include, but are not limited to, personal computers, servercomputers, hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, set top boxes, programmable consumerelectronics, mobile telephones, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices, and the like.

Embodiments of the aspects of the invention may be described in thegeneral context of data and/or processor-executable instructions, suchas program modules, stored one or more tangible, non-transitory storagemedia and executed by one or more processors or other devices.Generally, program modules include, but are not limited to, routines,programs, objects, components, and data structures that performparticular tasks or implement particular abstract data types. Aspects ofthe invention may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotestorage media including memory storage devices.

In operation, processors, computers and/or servers may execute theprocessor-executable instructions (e.g., software, firmware, and/orhardware) such as those illustrated herein to implement aspects of theinvention.

Embodiments of the aspects of the invention may be implemented withprocessor-executable instructions. The processor-executable instructionsmay be organized into one or more processor-executable components ormodules on a tangible processor readable storage medium which is not asignal. Aspects of the invention may be implemented with any number andorganization of such components or modules. For example, aspects of theinvention are not limited to the specific processor-executableinstructions or the specific components or modules illustrated in thefigures and described herein. Other embodiments of the aspects of theinvention may include different processor-executable instructions orcomponents having more or less functionality than illustrated anddescribed herein.

The order of execution or performance of the operations in embodimentsof the aspects of the invention illustrated and described herein is notessential, unless otherwise specified. That is, the operations may beperformed in any order, unless otherwise specified, and embodiments ofthe aspects of the invention may include additional or fewer operationsthan those disclosed herein. For example, it is contemplated thatexecuting or performing a particular operation before, contemporaneouslywith, or after another operation is within the scope of aspects of theinvention.

When introducing elements of aspects of the invention or the embodimentsthereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

In view of the above, it will be seen that several advantages of theaspects of the invention are achieved and other advantageous results maybe attained.

Not all of the depicted components illustrated or described may berequired. In addition, some implementations and embodiments may includeadditional components. Variations in the arrangement and type of thecomponents may be made without departing from the spirit or scope of theclaims as set forth herein. Additional, different or fewer componentsmay be provided and components may be combined. Alternatively or inaddition, a component may be implemented by several components.

The above description illustrates the aspects of the invention by way ofexample and not by way of limitation. This description enables oneskilled in the art to make and use the aspects of the invention, anddescribes several embodiments, adaptations, variations, alternatives anduses of the aspects of the invention, including what is presentlybelieved to be the best mode of carrying out the aspects of theinvention. Additionally, it is to be understood that the aspects of theinvention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The aspects of theinvention are capable of other embodiments and of being practiced orcarried out in various ways. Also, it will be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

Having described aspects of the invention in detail, it will be apparentthat modifications and variations are possible without departing fromthe scope of aspects of the invention as defined in the appended claims.It is contemplated that various changes could be made in the aboveconstructions, products, and methods without departing from the scope ofaspects of the invention. In the preceding specification, variouspreferred embodiments have been described with reference to theaccompanying drawings. It will, however, be evident that variousmodifications and changes may be made thereto, and additionalembodiments may be implemented, without departing from the broader scopeof the aspects of the invention as set forth in the claims that follow.The specification and drawings are accordingly to be regarded in anillustrative rather than restrictive sense.

What is claimed is:
 1. A treatment system for treating an aqueous liquidcomprising: a conduit for channeling the aqueous liquid to be treated; atreatment device associated with the conduit for altering the aqueousliquid and having an input port for receiving a treatment signalindicative of an extent to which the treatment device alters the aqueousliquid; a sensor sensing a parameter of the aqueous liquid and having ananalog output port providing an analog signal indicative of the sensedparameter, said sensor having a calibration memory device storingdigital information indicative of a calibration of the sensor and havinga digital output port providing a digital signal indicative of thedigital information; and a controller having a digital input portconnected to the digital output port of the sensor, said controllerreceiving the digital signal via its digital input port and determininga calibration of the sensor, said controller having an analog input portconnected to the analog output port of the sensor, said controllerreceiving the analog signal via its analog input port and determiningthe parameter of the aqueous liquid based on the received analog signaland based on the received digital signal, said controller having anoutput port connected to the treatment device providing the treatmentsignal to the input port of the treatment device, said treatment signalconfigured to control the treatment device as a function of thedetermined parameter by controlling the extent to which the treatmentdevice alters the aqueous liquid.
 2. The treatment system of claim 1wherein: the treatment device comprises a chlorine supplier for addingfree chlorine to the aqueous liquid and wherein the treatment signal isindicative of an amount of free chlorine added to the aqueous liquid oris indicative of a rate at which free chlorine is added to the aqueousliquid; the sensor comprises a chlorine sensor sensing a free chlorinelevel of the aqueous liquid wherein the calibration memory device storesdigital information indicative of a temperature-adjusted calibration ofthe chlorine sensor and wherein the analog signal is indicative of thefree chlorine level of the aqueous liquid; further comprising atemperature sensor for sensing a temperature of the aqueous liquid andhaving an output port providing a temperature signal indicative of thesensed temperature, wherein the controller has an input port forreceiving the temperature signal, and wherein the controller determinesthe temperature of the aqueous liquid based on the temperature signal;said controller determining the temperature-adjusted free chlorine levelof the aqueous liquid based on the received analog signal, the receivedtemperature signal, and based on the received digital signal, saidtreatment signal provided by the output port of the controller isconfigured to control the chlorine supplier as a function of thedetermined temperature-adjusted free chlorine level of the aqueousliquid as compared to a minimum free chlorine level by controlling theamount of free chlorine added to the aqueous liquid by the chlorinesupplier or the rate at which free chlorine is added to the aqueousliquid by the chlorine.
 3. The treatment system of claim 1 wherein: thetreatment device comprises an acid supplier for adding acid to theaqueous liquid and wherein the treatment signal is indicative of anamount of acid added to the aqueous liquid or is indicative of a rate atwhich acid is added to the aqueous liquid; the sensor comprises a pHsensor sensing hydrogen ions of the aqueous liquid wherein thecalibration memory device stores digital information indicative of atemperature-adjusted calibration of the pH sensor and wherein the analogsignal is indicative of the pH level of the aqueous liquid; furthercomprising a temperature sensor for sensing a temperature of the aqueousliquid and having an output port providing a temperature signalindicative of the sensed temperature, wherein the controller has aninput port for receiving the temperature signal, and wherein thecontroller determines the temperature of the aqueous liquid based on thetemperature signal; said controller determining the temperature-adjustedpH level of the aqueous liquid based on the received analog signal, thereceived temperature signal, and based on the received digital signal,said treatment signal provided by the output port of the controller isconfigured to control the acid supplier as a function of the determinedtemperature-adjusted pH level of the aqueous liquid as compared to amaximum pH level by controlling the amount of acid added to the aqueousliquid by the acid supplier or the rate at which acid is added to theaqueous liquid by the acid supplier.
 4. The treatment system of claim 1wherein: the treatment device comprises a chlorine supplier for addingfree chlorine to the aqueous liquid and wherein the treatment signal isindicative of an amount of free chlorine added to the aqueous liquid oris indicative of a rate at which free chlorine is added to the aqueousliquid; the sensor comprises a ORP sensor responsive to a free chlorinelevel of the aqueous liquid to provide a millivolt signal indicative ofan oxidizing power of the aqueous liquid wherein the calibration memorydevice stores digital information indicative of a temperature-adjustedcalibration of the ORP sensor; further comprising a temperature sensorfor sensing a temperature of the aqueous liquid and having an outputport providing a temperature signal indicative of the sensedtemperature, wherein the controller has an input port for receiving thetemperature signal, and wherein the controller determines thetemperature of the aqueous liquid based on the temperature signal; saidcontroller determining the temperature-adjusted oxidizing power of theaqueous liquid based on the received analog signal, the receivedtemperature signal, and based on the received digital signal, saidtreatment signal provided by the output port of the controller isconfigured to control the chlorine supplier as a function of thedetermined temperature-adjusted oxidizing power of the aqueous liquid ascompared to a minimum millivolt signal level by controlling the amountof free chlorine added to the aqueous liquid by the chlorine supplier orthe rate at which free chlorine is added to the aqueous liquid by thechlorine supplier.
 5. The treatment system of claim 1 wherein: thesensor comprises a TDS sensor sensing a TDS ppm salt level of theaqueous liquid and wherein the analog signal is indicative of the TDSppm salt level of the aqueous liquid; said controller determining theTDS ppm salt level of the aqueous liquid based on the received analogsignal and based on the received digital signal, said controllerproviding an indication when the determined TDS ppm salt level of theaqueous liquid is greater than a maximum.
 6. The system of claim 1wherein the calibration memory device comprises an EEPROM storing thefollowing information: a high or low gain, an offset, and ananalog-to-digital conversion value of the analog signal indicative ofthe sensed parameter.
 7. The system of claim 1 wherein the calibrationmemory device comprises an EEPROM storing the following information: twoor more temperature coefficients for adjusting the analog signalindicative of the sensed parameter.
 8. The system of claim 1 wherein thecalibration memory device comprises an EEPROM storing identificationinformation uniquely identifying the sensor.
 9. The system of claim 1wherein the controller includes a controller calibration memory devicein which the controller stores the digital information stored in thecalibration memory device of the sensor.
 10. The system of claim 1wherein the controller is configured to calibrate the sensor in theevent that the digital information stored in the calibration memorydevice of the sensor is not valid.
 11. The system of claim 1 wherein thecontroller is configured with a memory device having default calibrationinformation in the event that the digital information stored in thecalibration memory device of the sensor is not valid.
 12. The system ofclaim 1 wherein the digital information stored in the calibration memorydevice of the sensor is encrypted and wherein the controller isconfigured to decrypt the encrypted digital information.
 13. The systemof claim 1 wherein a controller memory device of the controller stores aplurality of identification information identifying selected sensors andwherein the controller is configured to disable an operation of thesystem if the calibration memory device of the sensor having its digitaloutput port connected to the digital input port of the controller doesnot have identification information which corresponds to theidentification information stored in the controller memory device.
 14. Atreatment system for treating an aqueous liquid comprising: a conduitfor channeling the aqueous liquid to be treated; a treatment deviceassociated with the conduit for altering the aqueous liquid and havingan input port for receiving a treatment signal indicative of an extentto which the treatment device alters the aqueous liquid; a sensorsensing a first parameter of the aqueous liquid and having an analogoutput port providing a first analog signal indicative of the sensedfirst parameter, said sensor sensing a second parameter of the aqueousliquid and having providing a second analog signal at the analog outputport indicative of the sensed second parameter, said sensor having acalibration memory device storing digital information indicative of acalibration of the first parameter relative to the second parameter andhaving a digital output port providing a digital signal indicative ofthe digital information; and a controller having a digital input portconnected to the digital output port of the sensor, said controllerreceiving the digital signal via its digital input port and determininga calibration of the sensor, said controller having an analog input portconnected to the analog output port of the sensor, said controllerreceiving the first and second analog signals via its analog input portand determining the first parameter of the aqueous liquid relative tothe second parameter based on the received analog signals and based onthe received digital signal, said controller having an output portconnected to the treatment device providing the treatment signal to theinput port of the treatment device, said treatment signal configured tocontrol the treatment device as a function of the determined parameterby controlling the extent to which the treatment device alters theaqueous liquid.
 15. The treatment system of claim 14 wherein the sensorcomprises at least one of: (a) a chlorine sensor so the first parameteris current signal indicative of a free chlorine of the aqueous liquid,(b) an ORP sensor so that the first parameter is a voltage signalindicative of free chlorine of the aqueous liquid, or (c) a pH sensor sothat the first parameter is current signal indicative of a pH of theaqueous liquid; and wherein the sensor further comprises a temperaturesensing device so that the second parameter is a signal indicative of atemperature of the aqueous liquid.
 16. The treatment system of claim 15wherein the sensor comprises a thermistor so that the second parameteris a signal indicative of a resistance of the thermistor which isindicative of a temperature of the aqueous liquid.
 17. A sensing devicecomprising a sensor configured to sense a first parameter and a secondparameter of a liquid and having an analog output port configured toprovide a first analog signal indicative of the sensed first parameterand configured to provide a second analog signal indicative of thesensed second parameter, said sensor having a calibration memory devicestoring individual digital information indicative of a calibration ofthe first parameter relative to the second parameter and having adigital output port providing a digital signal indicative of the digitalinformation.
 18. The device of claim 17 in combination with a treatmentsystem for treating an aqueous liquid, said treatment system comprising:a conduit for channeling the aqueous liquid to be treated; a treatmentdevice associated with the conduit for altering the aqueous liquid andhaving an input port for receiving a treatment signal indicative of anextent to which the treatment device alters the aqueous liquid; and acontroller having a digital input port connected to the digital outputport of the sensor, said controller receiving the digital signal via itsdigital input port and determining a calibration of the sensor, saidcontroller having an analog input port connected to the analog outputport of the sensor, said controller receiving the analog signals via itsanalog input port and determining the first parameter relative to thesecond parameter based on the received analog signals and based on thereceived digital signal, said controller having an output port connectedto the treatment device providing the treatment signal to the input portof the treatment device, said treatment signal configured to control thetreatment device as a function of the determined parameter bycontrolling the extent to which the treatment device alters the aqueousliquid.
 19. The device of claim 17 wherein the liquid is an aqueousliquid and wherein the sensor comprises a thermistor sensing temperatureproviding the second analog signal and a chlorine sensor providing thefirst analog signal comprising a gold cathode and a platinum anode, theplatinum anode being sealed within a tube comprising a proton exchangemembrane, wherein the tube provides a barrier to oxygen and anions fromthe environment exterior to the tube except as may pass through thetube.
 20. The device of claim 17 wherein the liquid is an aqueous liquidand wherein the sensor comprises a thermistor sensing temperatureproviding the second analog signal and a pH sensor providing the firstanalog signal comprising: (i) a gel-filled reference electrode; and (ii)a sensing electrode of antimony/antimony oxide or bismuth/bismuth oxidehaving an electroactive surface sealed within a tube comprising a protonexchange membrane that provides a barrier for the sensing electrode toboth oxygen and anions from the environment exterior to the tube. 21.The device of claim 17 wherein the liquid is an aqueous liquid andwherein the sensor comprises a thermistor sensing temperature providingthe second analog signal and a halogen sensor providing the first analogsignal comprising a metal anode shielded by a low electrical resistance,water-permeable, oxygen barrier comprising a tube comprising a protonexchange membrane that provides a barrier for the sensing electrode toboth oxygen and anions from the environment exterior to the tube. 22.The device of claim 17 wherein the liquid is an aqueous liquid andwherein the sensor comprises a total dissolved solids (TDS) sensorcomprising: a pair of spaced-apart electrodes configured to be excitedby a sine wave voltage; a current amplifier and rectifier electricallyresponsive to the pair of spaced-apart electrodes configured to generatea voltage indicative of the voltage between the spaced-apart electrodes;a converter electrically responsive to the voltage indicative of thevoltage between the spaced-apart electrodes configured to convert theindicative voltage for at least one of display and processing; a displayelectrically responsive to the converter configured to display a totaldissolved solids measurement in aqueous liquid in which the pair ofspaced apart electrodes is placed.
 23. The device of claim 17 whereinthe liquid is an aqueous liquid and wherein the sensor comprises athermistor sensing temperature providing the second analog signal and anORP sensor providing the first analog signal comprising a gold cathodeand a platinum anode, the platinum anode being sealed within a tubecomprising a proton exchange membrane, wherein the tube provides abarrier to oxygen and anions from the environment exterior to the tubeexcept as may pass through the tube.